The broad objective of the proposed research is to understand the mechanism for increases in dental caries observed in man and experimental animals ingesting elevated quantities of the trace mineral selenium. Specifically, we plan to determine the chemical forms of selenium in human teeth using dialysis techniques used in previous experiments with rodents. By the use of radioactively tagged selenium we plan to test if ncreasing levels of dietary selenium cause proportionate increases in the selenium concentrations in teeth and in the amounts of the different chemical forms of selenium in enamel and dentine of rats. We plan to characterize the principal factors involved in the development of selenium-induced dental caries by measuring dental caries in rats exposed to a high sucrose diet and elevated levels of dietary selenium. We will also test if selenium alters the mineralization of enamel by making scanning electron microscope pictures, inorganic composition measurements, microhardness determinations, acid solubility tests and molar tooth morphology measurements on the enamel from our experimental animals.